Conventionally, a valuable sheet-like document such as a paper sheet or a photograph is usually covered with a protective film for protection because such a sheet-like document is readily suffered from damage or breakage.
A process for laminating a sheet-like document between two pieces of plastic films by using a laminating apparatus will be described as follows. First of all, an article of a sheet-like document intervening between two plastic films is fed into the laminating apparatus by a pair of heating rollers. Then, the article is simultaneously heated and pressed by the heating rollers and thus the plastic films are softened. Afterwards, the sheet-like document is bonded with the softened plastic films to form a laminate structure.
The conventional laminating apparatus, however, lacks a thickness detecting mechanism. Regardless of the thickness of the article to be laminated, the working temperature and the rotating speed of the heating rollers are maintained constant. In a case that the sheet-like document is too thick or too thin, the laminating operation is readily suffered from failure. Generally, as the thickness of the sheet-like document is increased, an increased working temperature or a decreased rotating speed is required to soften the plastic films. If the working temperature of the heating rollers is insufficient or the rotating speed of the heating rollers is too fast, the plastic films are not completely softened and thus the sheet-like document fails to be bonded with the plastic films to form a laminate structure. On the other hand, as the thickness of the sheet-like document is reduced, a decreased working temperature or an increased rotating speed is required to soften the plastic films. If the working temperature of the heating rollers is too high or the rotating speed of the heating rollers is too slow, the plastic films are over-softened and thus readily adhered to the heating rollers. Under this circumstance, a so-called jamming phenomenon is resulted.
Therefore, there is a need of providing a laminating apparatus having a thickness detecting mechanism for detecting the thickness of the article to be laminated so as to dynamically adjust the working temperature or the rotating speed of the heating rollers of the laminating apparatus.